I am not sure if you want field trials or hunt test info, so I will include every level.
Working Certificate (Labrador Club) is an instinct test, dog must go and bring back one MARK (bird that the dog sees fall) on land and bring it back close to you. And then the dog must retrieve 2 single marks on water. Distances are close usually 40-60 yards with light cover.
Junior Hunter (Hunt Test AKC) Dog must pass 4 tests, each test will be 2 land marks and 2 water marks (each mark is run seperately). Dog must deliever to hand and must have reasonable line manners. Distance is anything up to 100 yards.
Senior Hunter (Hunt Test AKC) dog must pass 4 tests (1 double land) (1 double water) (1 water blind) (1 Land Blind) Doubles are two birds being shot and then the dog is sent to retrieve. Blinds are "planted" birds that the dog doesn't see. You must direct the dog to using whistle and hand signals. The dog should be under your control at all times, the dog does not go out and hunt it up you direct him exactly to it. At this level you must also honor (have your dog watch another dog work with out moving) and must be steady at the line. (not go till you send him)
Derby (Field Trial AKC) first level of field trials (no dogs 2 years or older are allowed) Typically senior type work but with longer distances up to 400+yards.
Qualifier (Field Trial AKC) harder level open to all dogs, Harder doubles, triples etc.
MAster Hunter (Hunt Test AKC) top level of hunt tests. typically see triples and hard doubles on water,land and water land combo's. Blinds are harder. Distance held to 100 yards more cover etc.
Open (Field Trial AKC) very hard tests again up to 400+yards.
Hunt Tests judge dogs against a standard of what they should be able to do at each level. It is possible for every dog to pass a Hunt test or no dgos to pass.
Field trials are looking for a winner. They are looking for the best dog that day they will give out placements for 1st, 2nd, 3rd, 4th. You get points for placements when you get 15 points you get an FC or AFC (Field Championship).
I am sure you still have questions and the best thing to do would be go watch both a field trial and a hunt test. the season starts in the spring. Or I would find the local club and see if they have training groups/classes you can join.
Light, "weedy" individuals are definitely incorrect; equally objectionable are cloddy lumbering specimens. Labrador Retrievers shall be shown in working condition well-muscled and without excess fat. Females should weigh between 55 and 70lbs and Males between 65 and 80lbs. Height females 21.5 to 23.5 inches males 22.5 to 24.5 inches at the withers.
HR Greenwoods Sealion Tsunami SH "Wave" born 3-9-2010
Greenwoods Amber Wave VCD2 RA SH AX OF WCX CGC "Amber" born 4-13-2005